The present invention relates to a brake pressure generator for an automotive brake system, wherein a booster piston displaceable by an auxiliary hydraulic pressure, in the direction of actuation is adapted to mechanically strike an annular piston and is displaceable in the direction of actuation. A master cylinder piston is sealingly guided within that annular piston to confine at least one working chamber separable from an unpressurized supply reservoir by way of a valve arrangement controllable in way-responsive manner, with the annular piston being of a stepped-piston configuration and having a section facing the pedal actuation which is of a smaller diameter.
Systems characterized by the foregoing features are known. In these systems, the brake pressure generator comprises a hydraulic booster in the pressure chamber of which is adjustable, by way of a brake valve, an auxiliary hydraulic pressure proportional to the actuating force respectively exerted on the brake pedal. A component part of the hydraulic booster is a booster piston sealingly and displaceably disposed in a bore of the hydraulic booster to displace a master cylinder piston in the direction of actuation as soon as an adequately high pressure has built up in the pressure chamber of the hydraulic booster.
The master cylinder piston, in turn, is sealingly guided in an axially displaceable manner in an annular piston, whereas the open end of the annular piston, facing away from the pedal is sealingly disposed in an axially displaceable manner on another piston so as to confine a working chamber by the annular piston, the master cylinder piston and the piston getting into contact with the opened end of the annular piston, which working chamber, normally, is in communication with an unpressurized supply reservoir through a brake valve disposed in the master cylinder piston. Conversely, the said working chamber is in communication with the wheel brake of a vehicle wheel to be decelerated.
If in the aforedescribed brake system an operating force is applied to the brake pedal, a hydraulic pressure will build up in the pressure chamber of the hydraulic booster which, above a predetermined pressure level, causes a displacement of the booster piston in the actuating direction involving an axial displacement of the master cylinder piston within the annular piston. It is already with a minor axial displacement of the master cylinder that the central valve disposed within the master cylinder piston is closed to thereby block a hydraulic connection between the unpressurized supply reservoir and the working chamber of the brake pressure generator. In a further displacement of the master cylinder piston, the working chamber is pressurized to thereby supply a corresponding hydraulic pressure to the wheel brake of the vehicle wheel to be decelerated, causing a brake effect to take place.
After the booster piston and the master cylinder piston, respectively having performed a structurally predetermined movement of displacement and after a corresponding hydraulic pressure having built up in the working chamber of the brake pressure generator, the booster piston will get into abutment with an annular shoulder of the annular piston to simultaneously displace the latter in the actuating direction. The displacement of the annular piston does not offer any substantial force against the pedal movement as the front face of the annular piston facing away from the brake pedal is exposed to a space normally in communication with an unpressurized supply reservoir. An auxiliary hydraulic pressure may be applied to the space confined by the front face of the annular piston, facing away from the pedal, in predetermined brake situations, via corresponding valve means, so that in given conditions, restoring of the booster piston of the hydraulic booster might occur.
In the foregoing, the hydraulic pressure built up in the working chamber is directly proportional to the displacement travel of the master cylinder piston. As the displacement travel of the master cylinder piston as a result of the mechanical coupling to the booster piston of the hydraulic booster also is proportional to the displacement travel of the booster piston, on the one hand, correspondingly large displacement movements of the booster piston of the hydraulic booster are required whereas, on the other hand, relatively large diameters will have to be selected for the master cylinder piston in order to feed a corresponding pressure fluid volume to the wheel brakes.
It is therefore an object of the present invention to configure a brake pressure generator of the type described in such a manner so as to cause, with an intact external energy supply, in a short displacement travel of the booster piston a relatively high pressure rise in the working chamber of the brake pressure generator.